Origins of Negative and Positive Electromechanical Response of Oligopeptide Piezoelectrics

In response to an applied electric field, materials and even individual molecules can exhibit electromechanical response. Previous work has demonstrated the piezoelectric distortion of polar organic crystals, biomaterials, and even single molecular monolayers, increasing length in response to the change in potential energy of interaction between the polarization or dipole moment and the applied electric field. In this work, we demonstrate through density functional calculations that helical oligopeptides, depending on sequence can exhibit both positive and surprisingly also negative piezoresponse. While the overall molecular dipole moment may favor positive piezoresponse, individual hydrogen bonding interactions along the backbone have the opposite direction, enabling tailored sequences to yield either net expansion or contraction in response to an electric field. While negative piezoresponse has largely been considered in polyvinylidene difluoride (PVDF) and related systems, understanding the atomic and molecular basis for both electromechanical effects will yield interesting new applications.